Wireless communications is becoming increasingly important, with wireless systems finding their way into ever growing numbers of applications. Wireless systems have become ubiquitous in the military environment.
Many wireless communications system use encryption to protect communicated data from unauthorized interception. In an encryption system, the message to be hidden (sometimes called “plaintext”) is modified in a reversible way (by a process sometimes referred to as “encryption”) such that the substance of the message is hidden. The resulting encrypted message (sometimes called “ciphertext”) can then be transmitted across an unsecured (subject to eavesdropping or interception) channel. Upon reception, the original message is recovered by reversing the modification (by a process sometimes referred to as “decryption”). Of course, to ensure that only the desired recipient can properly decrypt the encrypted message, some aspect of the encryption algorithm is kept secret. Typically, the encryption algorithm operates using a key which is kept secret while the details of the algorithm may be publicly disclosed. Distribution of the key is limited to those authorized to receive the messages that are encrypted with the key.
Distribution of keys in a secure manner is a difficult aspect in encrypted communications. Clearly, distribution of keys through an unsecured channel is undesirable, since an eavesdropper can obtain the key and then decrypt any subsequent encrypted communications using that key. Accordingly, in many communications systems, it is necessary to distribute keys through some other means outside the communication system. Typically, personnel and equipment which handle the keys must also be authorized to receive the messages that are encrypted. For example, for protection of classified information, the keys, materials on which the keys are stored, and systems which have keys loaded within all must be handled as classified items. Accordingly, distribution of keys can be quite tedious. While some schemes, such as public key cryptosystems, attempt to reduce difficulties of key distribution (e.g., using asymmetric encryption and decryption algorithms), such schemes often do not work well in unidirectional and multicast environments. Even when such schemes work for the intended use, distribution of the private keys and certificates can remain difficult.
In an encrypted communications system, it is often desirable to change keys frequently. This can be part of regular security measures which dictate that it is undesirable to transmit too much information using the same key. Changing keys may also be necessary if a node has been compromised in some way that might result in the key being available to an unauthorized eavesdropper. Of course, changing keys complicates the key distribution problem, as new keys must periodically be distributed to users of the system.
The aforementioned challenges in encrypted communications are multiplied when communications nodes are located in remote or unmanned areas. For example, increasing use of unmanned air vehicles (UAVs) and unmanned ground vehicles (UAGs) is being made. Once a UAV or UAG begins an operational mission, access to the UAV or UAG to load in new keys is sometimes not possible.